1. Field of the Invention
This invention relates to a splicing mechanism on a roll changing apparatus for cutting and transferring a moving web to a new core without stopping movement of the web. In particular, this invention relates to a method and apparatus for splicing the moving web without causing a fold-back or wrinkling of the web on the new core.
2. Background of the Related Technology
Many commercial and industrial laminating, coating and film processing operations are conducted on high speed web handling equipment which operate continuously for long periods of time. Paper converting is one example of such an operation. At the end of the processing line the web is wound lengthwise into a large parent roll or mill roll of material. In the processing of web materials, it is inefficient to stop the entire operation each time an individual roll of material needs to be changed. For this reason, rewinding devices have been developed for cutting and transferring a moving web so that successive rolls of material may be continuously wound without interrupting the operation.
One such rewind device, commonly referred to as either a turnover rewind stand or turret rewinder, is disclosed in U.S. Pat. No. 3,529,785 assigned to the same assignee as the present invention. A turnover rewind stand includes a pair of rotatable spindles or spools to which the web may be affixed for rewinding purposes. The two spindles are mounted on a turret, and by revolving or "turning over" the turret, the spindle containing a fully wound roll of web material is moved out of the rewinding position and a new core is simultaneously moved into the rewinding position. Upon severing the web, the new leading edge of the web is affixed to the empty core to continue the rewinding of the web while the finished roll is removed from the rewind stand. This process may be repeated over and over in order to rewind a number of rolls successively for as long as the web processing line is operated.
The transfer of the web to a new core is typically accomplished by pressing or pasting the web against a new core which has been covered with a tacky adhesive, although other methods of affixing the web to the core exist. After the web is put in contact with the core, the web is severed with a knife at a point downline from the new core. The web is thereby rewound onto the new spindle.
Since this type of splicer involves cutting the web at a point after the web has passed the new core, this type of mechanism often causes the web to fold-back on itself on the new core when the splice is performed. This fold-back results in a double thickness of the web and wrinkling of the web at the core which is undesirable. While the affects of the fold-back may be alleviated after a number of revolutions on the new spindle, nonetheless the fold-back results in a significant amount of wasted material. It is therefore desirable to provide a web splicing device which will not produce a fold-back and instead the web material transferred to the new core should be fold and wrinkle-free from the very start.
Other devices have been developed in an effort to provide a "no-fold-back" transfer of a moving web, but such devices are very complex and expensive and their effectiveness is less than certain, especially on high speed operations. For example, U.S. Pat. No. 4,422,586 to Richard S. Tetro (The Black Clawson Company) discloses a device which causes the web to deflect into a knife in order to sever it and transfer it to a new roll. On the Tetro device, an adhesive strip is applied to the outer surface of a new core upon which the web is to be wound. A cutting blade is brought into close proximity to the new core. The web is then urged toward the new core so that the adhesive strip bonds to the surface of the web and furthermore causes the web to deflect slightly into the blade so that the web is severed at a point immediately adjacent to the adhesive strip. The leading edge of the severed web remains adhered to the adhesive strip so that the web may be wound onto a new core.
Despite the assertion in the Tetro patent that the device disclosed therein provides a no-fold-back transfer of the web, the fact of the matter is that the splice is made after the web passes the new core and that on at least some applications a fold-back does occur even though it may be a small one. More importantly, the device disclosed in the Tetro patent is limited in its application to relatively thin web materials. In operations involving thicker grades of material, it is difficult to create a sufficient deflection in order to sever the web utilizing the approach disclosed in the Tetro patent.
Another no-fold-back device available in the market is produced by IMD Corporation. The IMD device passes the web between two rotating rolls which contain a complex set of splicing and vacuum mechanisms for cutting and transferring the web onto a new core. Within one roll is a knife which is extendable outward from the surface of the roll. The second roll is provided with a cavity which the knife projects into. The second roll also has a vacuum chamber which includes a grid having a number of small holes on the outer surface of the roll immediately adjacent the cavity. The small holes in the grid are used to apply a vacuum to hold the web against the outer surface of the second roll. The rotation of the first and second rolls are timed so that the knife from the first roll projects into the cavity of the second roll to sever the web. The application of the vacuum is also timed so that it will hold the leading edge of the severed web against the second roll, then the vacuum is released so that the leading edge may be transferred to a third roll, i.e. the new core.
The timing of the cutting action of the knife is critical in order to sever the web, and the timing of the application and release of the vacuum is also critical in order to transfer the web to the new core. Both timing aspects are extremely difficult to achieve in high speed operations. Some web processing lines operate at over 1000 feet per minute. It is nearly impossible to extend and then retract the knife, and to apply and then release the vacuum, at the critical times and to do so quickly enough to attain high speeds. The use of a thick grade of web material causes further difficulties in using the IMD splicing process.